For the final touch you can use some manipulation of brightness/contrast to somewhat remove both blur on the original photo and the blur effect applied during the "make seamless" process, and you have it done.

PS The real texture is 2048x2048, only 512x512 was used for the purpose of this tutorial. ;-)

Wow, I'm shocked that GIMP smoothed out the seams for you and its not even noticeable. Is this GIMP 2.8?
I have it installed on my Fedora 16, I may try this out.
Such a cool feature and eliminates my hour of clone/stamp tool work